\"Counter-Petition\" in the case of Adultery

Like others have said, just go along with the divorce if the reasons for him saying UB aren't too outlandish. If divorce is inevitable then contesting everything costs money. After the nisi has been granted then you will need to delay the absolute until the financials are sorted.
The financials are a different matter. You'll need to go to mediation, if that fails then it's ancillary relief, which is going through the courts. It doesn't say if your friend has children, so it's hard to even guess what a court would help decide.
Use wikivorce wisely and you really can do a real lot yourself for nothing. I stopped using a solicitor as my ex was been very obstructive and I knew they'd escalate my costs.
If he's divorcing your friend, then unless she agrees to a financial settlement that gets rubber stamped by the courts, it's in his interests to get it sorted, otherwise there will always be a financial tie. What I would advise is her to apply for spousal maintenance if she's struggling financially now.